As is known, all electronic devices that include integrated circuits require at least one DC voltage supply and typically require multiple DC voltage supplies. A DC voltage supply may be generated from an AC voltage source (for example, 110 volts AC) or from another DC voltage supply (for example, a battery). To generate a DC voltage supply from an AC voltage, the AC voltage is processed in a controlled manner. For example, a switch-mode power supply will rectify the AC voltage to produce a DC bridge voltage. Using one of a plurality of switch mode converter topologies (for example, full bridge, half bridge, buck, or boost) an inductor is charged and discharged at a controlled rate to produce a regulated DC voltage supply.
Generally, analog-based circuitry is used to regulate the DC voltage supply at the desired voltage using feedback loops. Typically in such circuitry, a resistance divider network is coupled to the DC voltage supply to produce a representation of the DC output that is provided to a controlled circuit. The control circuit includes an operational amplifier, a saw tooth generator, and a comparator. The operational amplifier receives the representation of the DC output and a reference voltage to produce, therefrom, an error signal. The comparator receives the error signal and a saw tooth signal, which is produced from the saw tooth generator, and produces, therefrom, a pulse width modulation signal. The pulse width modulation signal controls the charging and discharging of the inductor. Depending on the overall gain of the power supply, the DC output can be regulated within a few milli-volts.
For mixed-signal integrated circuit devices having analog and digital circuitry, however, analog-based regulation circuitry has basic power requirements that can impact power conservation objectives for the device. These power conservation objectives translate to extending the battery lifespan of the devices. An example is to turn off circuitry or slow down the clock rate to that circuitry when it is not needed to support the present function. Another example is to put the device in a “sleep” mode when the entire device is not “in use.”
But the analog-based regulator has minimum power requirements to sustain operational characteristics such as the available headroom voltage, sustaining stability of the regulator components. Reducing the power below these minimum power requirements adversely affect the performance of the analog-based regulator and the integrated circuit device generally. Thus, these minimum power requirements of analog-based regulators can frustrate maximizing the battery lifespan of such devices.
Therefore, a need exists for a method and apparatus of regulating DC output supplies without the above-referenced limitations.